For power line communication (PLC) signals to pass through a conventional distribution transformer they need to be below about 3 kHz. By using the frequency band between 1 kHz and 3 kHz a communication channel can be established for which the range of the PLC signal is not limited by the distribution transformers. However, compared to PLC systems using higher frequencies (such as 132 kHz), the components needed to capacitively couple or transformer couple the PLC signal to the power line become prohibitively large.
Many modern electronic systems incorporate a power factor correction (PFC) circuit as part of the function of the power supply circuits. The PFC circuit's job is to generate the bulk voltage for rest of the system, and to shape the current waveform so that it tracks the incoming line voltage. By forcing the current to match the input voltage sine wave, the load the system presents to the line will look resistive and the power factor will be near 1.0. the power factor correction circuit conventionally does this by applying PWM control to a power MOSFET that is in series with an inductor across the line. A simplified schematic of one such approach is shown at 10 in FIG. 1.